The invention relates to a rock drill having a drill head fitted with a hard metal cutting edge, a chucking shank, and at least on transport coil of spiral-shaped construction.
The spiral-shaped transport coils of rock drills are produced by cutting or noncutting treatment in order to produce chip grooves in the generally cylindrical initial material.
In rock drills the transport coil has the main function of transporting the material detached by the hard metal cutting edge, that is to say the drilling dust or drillings, out of the drill hole. The size of the drilling dust groove, that is to say the clear transport cross-section, is then a decisive factor in the efficiency of the drill, that is to say, a good transport of drilling dust ensures good feed and prevents chatter marks in the drill hole and damage to the drill by jamming, overheating or the like. Jamming of the drill also involves danger of an accident to the operator. A large drilling dust transport groove with a corresponding configuration therefore ensures adequately good transport of drilling dust. This has a considerable influence on the useful life of the drilling tool.
The transport coil is also required to provide guidance characteristics in the drill hole to some extent.
In order to allow for adequate transport of the drilling dust, in known drills the transport groove cross-section is chosen so large that a ratio of diameters of the core diameter to the transport coil diameter of approximately 0.5 is obtained. Such a large transport groove cross-section to transport the drilling dust is necessary in the case of high capacity tools. However, a large transport groove cross-section has the disadvantage that the core of the transport coil is seriously weakened. When the drill locks, therefore, fractures always occur in the region of the core cross-section weakened by the transport groove. It is at least necessary to use very high-grade tool steel made of alloy steels in order to satisfy the strength requirements. The cross-section may be weakened additionally by core bores for coolant.
A drilling tool, also for use as a rock drill, tipped with a hard metal cutting edge, which has become known from German Pat. No. 6,933,778, consists of a rolled basic profile with two longitudinal ribs and its transport coil is produced by turning or twisting the basic profile. In a drilling tool of this type the ratio of coil diameter to the transport coil diameter is &gt;0.5, as is otherwise customary for rock drills. However, due to its configuration the transport coil formed by the twisted longitudinal ribs exhibits unsatisfactory transport characteristics for the drilling dust. Accumulation and jamming are experienced particularly, due to the small transport groove cross-section. The drilling characteristics of such a tool are far inferior as regards drilling dust transport compared to the normal drilling tools. This also applies to the tools according to DIN 20,377, July 1979.
A certain minimum amount of free transport cross-section is therefore necessary in order to obtain satisfactory transport power of the drilling dust in the transport coil, and this generally leads to a weakening of the core diameter of the transport coil and consequently necessitates expensive initial materials in order to reduce the risk of fracture.